Original source: New Scientist
It’s no Michael Phelps, but this tiny robot swims the front crawl at 10 micrometres per second. It would take about two months for it to swim a lap in an Olympic swimming pool – in that time, Phelps could swim almost 5 million lengths. But the bot is fast for its size and strong enough to get through viscous liquids, like blood, to deliver medicine from inside a vein.
The front crawl is the fastest way for humans to swim. So Tianlong Li at the Harbin Institute of Technology in China and his colleagues built their swimming robot to mimic that motion.
Each bot is 5 micrometres long and has three main parts linked by two silver hinges. Its gold body is flanked by two magnetic arms made of nickel. Alternating the direction of a magnetic field around the bot causes its arms to rotate and propels the nano-swimmer forward (Nano Letters, doi.org/b9wh).
“It’s exciting due to its speed and its really small size, just about the same size as a blood vessel,” says Eric Diller at the University of Toronto in Canada who researches micro-robots. “It’s small enough basically to go anywhere within the body.”
Because bodily fluids are more viscous and difficult to swim through than water, the researchers also tested their nano-swimmers in serum. The bots only swam 5.5 micrometres per second, but that’s still faster than many other similar mini-machines.
For targeted non-invasive medicine delivery, these nano-swimmers could be coated with medicine, injected into the bloodstream and roughly steered by external magnetic fields.
However, they are too small for just one to carry enough medicine to actually help. “Maybe a thousand of them would be necessary,” says Diller. “There’s no way to keep track of all of them, so there are a lot of questions about safety and toxicity.”
They will have to be made of biodegradable materials before they can be used in the bloodstream. But Diller says that bots for use in the urinary tract or the eyeballs could begin clinical trials within the next five to 10 years. Injecting a single swimmer into an eyeball to deliver medication directly to the retina and then removing the bot would be far simpler than letting a swarm of them swim through the entire circulatory system.
We don’t know how fast Phelps could swim in blood – thankfully, his recent race against a great white shark didn’t provide a testing ground. But since you can’t inject him into your bloodstream, these nano-swimmers will have to do.